MDX is a user-funded transportation agency dedicated to improving the mobility of people, goods, and the economy in Miami-Dade County. The not-for-profit agency was created in 1994 by the Miami-Dade County Commission to establish local control of toll revenues collected on the five MDX expressways, and to ensure that the toll revenue collected would be reinvested to improve transportation locally. MDX is a user-funded agency. The agency does not receive money from gasoline taxes or other tax revenue to maintain, operate and enhance its expressways. The MDX expressway system consists of five of the most heavily traveled expressways in Miami-Dade County: SR 112/Airport Expressway SR 836/Dolphin Expressway SR 874/Don Shula Expressway SR 878/Snapper Creek Expressway SR 924/Gratigny Parkway